1. Field of the Invention
The present invention relates to a thread tension control device for a sewing machine, said device is used for providing a stable tension to a thread by regulating the pressure applied to the thread interposed between a pair of tension discs.
2. Description of the Prior Art
As this kind of thread tension control device for a sewing machine, it is proposed, as disclosed in Japanese Utility Model Publication No. 7-52693, to provide an adequate tension to a thread by regulating the tension applied to the thread interposed between a pair of tension discs by using a pneumatic cylinder equipped with an air regulator.
In this thread tension control device proposed hitherto, a pair of tension discs are disposed on a tension stud fixed in part of the sewing machine main body. One tension disc of the pair of tension discs is fixed on the tension stud, and other tension disc is freely fitted on the tension stud slidably in its axial direction. This other slidable tension disc is engaged with a drive rod of the pneumatic cylinder. By moving the other tension disc to the fixed tension disc side through the action of the pneumatic cylinder, the thread engaged with the tension stud and interposed between the pair of tension discs is pressed and held.
Between the pneumatic cylinder and an air supply source, there is an air regulator composed of a variable type constant back pressure valve. When a back pressure regulating knob attached to the air regulator is manipulated, air pressure to be supplied to the pneumatic cylinder is regulated. By regulating this knob, it is designed to adjust the pressure to the thread held between the pair of tension discs, that is, to regulate the thread tension.
However, in the conventional thread tension control device for a sewing machine having such configuration, in order to check if the supply air pressure to the pneumatic cylinder is appropriate or not, the operator has to read the indication value of the pressure gauge connected to the air piping between the air regulator and pneumatic cylinder. As a result, to adjust the thread tension during operation of the sewing machine, the operation of the sewing machine must be stopped once, and its adjustment requires time and labor for manipulating the back pressure regulating knob and reading the indication value of the pressure gauge, and therefore the thread tension could not be adjusted instantly while continuing operation of the sewing machine.
In the case of other conventional thread tension control device combined with a pressure gauge and variable type constant back pressure valve equipped with a back pressure regulating knob, since the data of appropriate air pressure cannot be stored corresponding to the type or size of the thread, such complicated job is required every time the thread is changed.
The present invention is devised in the light of such background, and it is hence a primary object thereof to present a thread tension control device for a sewing machine capable of adjusting the thread tension instantly while continuing operation of the sewing machine by controlling the air pressure to an adequate value promptly depending on the type or size of the thread.
It is other object of the present invention to eliminate or to save markedly the time and labor every time thread is changed by effectively making use of the data of appropriate air pressure acquired in the past for adjustment of thread tension.
It is a further object of the present invention to release the thread tension instantly in addition to the foregoing objects.
To achieve the primary object, the tension control device for a sewing machine as set forth in claim 1 of the present invention has the following configuration. One end of a tension stud is fixed in part of the sewing machine main body. A pair of tension discs are disposed on the tension stud slidably in its axial direction, and are supported rotatably about the tension stud. A pneumatic cylinder has a drive rod, and the drive rod is engaged with at least one of the pair of tension discs. The drive rod moves one tension disc to other tension disc so that one tension disc is pressed to other tension disc. An air regulator is interposed between the pneumatic cylinder and an air supply source. The pressure to the thread engaged with the tension stud and held between the pair of tension discs is adjusted by the air regulator.
It is a feature of the present invention that the air regulator is composed in an electropneumatic system for converting between voltage and air pressure. As a result, the applied voltage to the electropneumatic air regulator is controlled on the basis of an instruction from a microcomputer, so that the set pressure of the air supplied to the pneumatic cylinder is adjusted.
According to the present invention as set forth in claim 1, since the electropneumatic air regulator is used as the air regulator, the applied voltage to the electropneumatic air regulator can be controlled on the basis of an instruction from the microcomputer. As a result, without spending any time in manipulation of the back pressure regulating knob or reading of pressure gauge, the set pressure of the air to be supplied to the pneumatic cylinder can be adjusted quickly and adequately. Therefore, without having to stop the operation of the sewing machine in thread tension adjustment, the thread tension can be adjusted instantly while continuing this operation.
In particular, as set forth in claim 2, using a pneumatic cylinder of dual action type, by connecting a solenoid valve to the air outlet side port of pneumatic cylinder and opening this solenoid valve on the basis of an instruction from the microcomputer, the pressure to the thread held between the pair of tension discs can be set free so that the thread can be released. Therefore, thread releasing action after specified sewing, and thread tension adjustment by controlling the air set pressure when resuming sewing operation can be done instantly.
Further, as set forth in claim 3, by storing data of control voltage to the electropneumatic air regulator in the microcomputer, and comprising memory means for reading out the data, when using the thread of the same type and size as the thread used in the past, the data of the appropriate air pressure acquired in the past adjustment can be effectively utilized. Therefore, it is possible to eliminate or to save markedly the time and labor for knob manipulation for adjusting the air pressure appropriately every time the thread is changed.
Moreover, as set forth in claims 4 and 5, when a pair of tension discs, the pneumatic cylinder and the electropneumatic air regulator are arranged in plural sets corresponding to a plurality of threads, the pressure to each thread by these plural sets of pair of tension discs can be controlled in batch by the action of the air regulator on the basis of an instruction from the microcomputer. Therefore, without requiring the complicated and labored operation for manipulating the back pressure regulating knob for every one of the plurality of threads, the tension adjustment for the plurality of threads can be controlled in batch by the microcomputer, and the applicability to the sewing machine using a plurality of threads simultaneously may be enhanced.